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2009-07-06 PIER Vol. 93, 385-401, 2009. doi:10.2528/PIER09031102

A New Look at Numerical Analysis of Uniform Fiber Bragg Gratings Using Coupled Mode Theory

Jiun-Jie Liau, Nai-Hsiang Sun, Shih-Chiang Lin, Ru-Yen Ro, Jung-Sheng Chiang, Chung-Long Pan, and Hung-Wen Chang

The coupled mode theory (CMT) is used to analyze uniform Fiber Bragg gratings. The multi-mode CMT is expressed as the first-order vector ordinary differential equations (ODEs) with coefficients depending on the propagation distance. We show in this paper that by changing variables, the original couple mode equations (CMEs) can be re-casted as constant coefficient ODEs. The eigenvalue and eigenvector technique (EVVT), the analytic method for solving constant coefficient ODEs, is then applied to solve the coupled mode equations. Furthermore, we also investigate the application of Runge-Kutta method (RKM) to the calculation of the global transfer-function matrix for CMEs. We compare the transmission and the reflection spectra obtained by EVVT with those by RKM. Both results agree within machine accuracy. Numerical simulations conclude that solving constant coefficient ODEs improves the speed and accuracy of solutions to the original CMEs.

2009-07-01 PIER Vol. 93, 369-384, 2009. doi:10.2528/PIER09060305

An Efficient Twofold Iterative Algorithm of FE-BI-MLFMA Using Multilevel Inverse-Based Ilu Preconditioning

Zhen Peng, Xin-Qing Sheng, and Fei Yin

It is known that the conventional algorithm (CA) of hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) usually suffers the problem of slow convergence, and the decomposition algorithm (DA) is limited by large memory requirement. An efficient twofold iterative algorithm (TIA) of FE-BI-MLFMA is presented using the multilevel inverse-based incomplete LU (MIB-ILU) preconditioning in this paper. It is shown that this TIA can offer a good balance of efficiency between CPU time and memory requirement. The tree-cotree splitting technique is then employed in the TIA to further improve its efficiency and robustness. A variety of numerical experiments are performed in this paper, demonstrating that the TIA exhibits superior efficiency in memory and CPU time to DA and CA, and greatly improves the computing capability of FE-BI-MLFMA.

2009-06-29 PIER Vol. 93, 355-367, 2009. doi:10.2528/PIER09050605

A Reconfigurable U-Koch Microstrip Antenna for Wireless Applications

Ali Halim Ramadan, Madi Mervat, Ali El-Hajj, Shahwan Khoury, and Mohammed Al-Husseini

In this paper, a low-cost multiband printed-circuit-board (PCB) antenna that employs Koch fractal geometry and tunability is demonstrated. The antenna is fabricated on a 1.6 mm-thick FR4-epoxy substrate with dimensions 4 cm × 4.5 cm, is microstrip-line fed and has a partial ground plane flushed with the feed line. The proposed antenna is simulated using the Finite-Element Method for three different switching cases and the return loss is measured for each case. It is shown that the antenna can cover the bands of several applications including 3G, WiFi, WiMAX as well as a portion of the UWB range. The radiation patterns are satisfactorily omnidirectional across the antenna's operation bands.

2009-06-24 PIER Vol. 93, 339-354, 2009. doi:10.2528/PIER09051103

Numerical Solution of Scattering from Thin Dielectric-Coated Conductors Based on Tds Approximation and EM Boundary Conditions

Shiquan He, Zai-Ping Nie, and Jun Hu

Thin dielectric sheet (TDS) approximation and electromagnetic (EM) boundary conditions are considered together to derive out a set of integral equations as an alternative to the impedance boundary condition (IBC) method to solve the electromagnetic scattering from thin dielectric-coated conductors. Only with discretizing the induce current on the conductor surfaces and solving an integral equation similar to that for a PEC, the scattering fields from the whole coating system (electric or magnetic material coating) are computed. Both the electric field integral equation (EFIE), magnetic field integral equation (MFIE) and their combination form are presented. These equations are converted to a matrix equation by Galerkin's method and then solved with multilevel fast multipole algorithm (MLFMA) to obtain the far fields scattering from these coated objects.

2009-06-22 PIER Vol. 93, 323-337, 2009. doi:10.2528/PIER09052503

Linearization Error in Electrical Impedance Tomography

Nick Polydorides

In electromagnetic tomography and resistivity survey a linearized model approximation is often used, in the context of regularized regression, to image the conductivity distribution in a domain of interest. Due to the error introduced by the simplified model, quantitative image reconstruction becomes challenging unless the conductivity is sufficiently close to a constant. We derive a closed form expression of the linearization error in electrical impedance tomography based on the complete electrode model. The error term is expressed in an integral form involving the gradient of the perturbed electric potential and renders itself readily available for analytical or numerical computation. For real isotropic conductivity changes with piecewise uniform characteristic functions the perturbed potential field can be shown to satisfy Poisson's equation with Robin boundary conditions and interior point sources positioned at the interfaces of the inhomogeneities. Simulation experiments using a finite element method have been performed to validate these results.

2009-06-22 PIER Vol. 93, 307-322, 2009. doi:10.2528/PIER09052610

A Heterodyne Six-Port FMCW Radar Sensor Architecture Based on Beat Signal Phase Slope Techniques

Bouraima Boukari, Emilia Moldovan, Sofiene Affes, Ke Wu, Renato G. Bosisio, and Serioja Ovidiu Tatu

A Heterodyne six-port FMCW collision avoidance radar sensor configuration based on beat signal phase slope techniques is presented in this paper. Digital IF circuitry has been used in order to avoid problems related to DC offset and amplitude and phase imbalance. Simulations show that the velocity and range to the target is obtained simultaneously, with very good accuracy. Results are compared to other techniques and system architectures.

2009-06-22 PIER Vol. 93, 291-306, 2009. doi:10.2528/PIER09031702

Vector Hopkins Model Research Based on off -Axis Illumination in Nanoscale Lithography

Pengfei Cao, Lin Cheng, and Xiaoping Zhang

Based on vector electromagnetic theory and the Waveguide Model, the vector Hopkins model is deduced. The model contains the vector Hopkins formula and the resist profile model of fast Optical Proximity Correction. The vector Hopkins formula considers incidence angles and azimuth angles of off-axis illumination, which differs from the traditional scalar Hopkins formula. The resist profile model is employed to analyze the effect of the photoresist diffusion under off-axis illumination by using self-adaptive Gaussian filter with scale adjustable, and a new transmission cross coefficient is obtained. The projection system parameters are introduced simultaneously, such as incidence angles, azimuth angles of off-axis illumination and diffusion parameters of photoresist. By simulating the aerial image of 3D mask in the actual lithography process, the optimal angular range of oblique incidence is studied; the image quality by impact with the oblique incidence angle is discussed as well.

2009-06-19 PIER Vol. 93, 275-289, 2009. doi:10.2528/PIER09050606

A Metamaterial-Based E-Plane Horn Antenna

Ruey-Bing Hwang, Hung-Wang Liu, and Cheng-Yuan Chin

In this paper, we reported an E-plane horn antenna incorporating a metamaterial. Such a metamaterial is made up of metallic cylinders organized in a two-dimensional square lattice. After properly designing the lattice constant and unit cell pattern, we synthesized a medium with the effective refractive index smaller than unity. Therefore, once the waves were excited within the metamaterial, the refractive waves tend to be perpendicular to the interface between the metamaterial and uniform medium. Based on this concept, a 4-way beam splitter was designed to equally distribute the input power into 4 different directions. We then guide each of the power into individual E-plane flared opening to radiate a directional beam pattern in each sector. We have fabricated this antenna and measured its radiation characteristics including the return loss and far-field pattern. The excellent agreement between the measured and simulated results was obtained. Due to the properties of robust, low-loss, and low-cost, this antenna may have promising application in a point-to-multiple-point downlink system.

2009-06-18 PIER Vol. 93, 255-274, 2009. doi:10.2528/PIER09041004

Retrieving the Green's Function from Cross Correlation in a Bianisotropic Medium

Evert C. Slob and Kees Wapenaar

Development of theory and experiments to retrieve Green's functions from cross correlations of recorded wave fields between two receivers has grown rapidly in the last seven years. The theory includes situations with flow, mechanical and electromagnetic disturbances and their mutual coupling. Here an electromagnetic theory is presented for Green's function retrieval from cross correlations that incorporates general bianisotropic media, which is the most general class of linear media. In the presence of dispersive non-reciprocal media, the Green's function is obtained by cross correlating the recordings at two locations of fields generated by sources on a boundary. The only condition for this relation to be valid is that the medium is non-dissipative. The principle of bianisotropic Green's function retrieval by cross correlation is illustrated with a numerical example.

2009-06-15 PIER Vol. 93, 237-254, 2009. doi:10.2528/PIER09042204

Grey Prediction Based Particle Filter for Maneuvering Target Tracking

Jun-Feng Chen, Zhi-Guo Shi, Shao-Hua Hong, and Kang Chen

For maneuvering target tracking, we propose a novel grey prediction based particle filter (GP-PF), which incorporates the grey prediction algorithm into the standard particle filter (SPF). The basic idea of the GP-PF is that new particles are sampled by both the state transition prior and the grey prediction algorithm. Since the grey prediction algorithm is a kind of model-free method and is able to predict the system state based on historical measurements other than establishing a priori dynamic model, the GP-PF can significantly alleviate the sample degeneracy problem which is common in SPF, especially when it is used for maneuvering target tracking. Simulations are conducted in the context of two typical maneuvering motion scenarios and the results indicate that the overall performance of the proposed GP-PF is better than the SPF and the multiple model particle filter (MMPF) when the tracking accuracy, computational complexity and tracking lost probability are considered. The performance improvements can be attributed to that the GP-PF has both model-based and model-free features.

2009-06-13 PIER Vol. 93, 221-236, 2009. doi:10.2528/PIER09050407

Composite Compact Triple-Band Microstrip Antennas

Majeed Alkanhal

Two new triple band small size composite-resonator microstrip antenna configurations for wireless communications are presented in this paper. The proposed antennas, each is built of three resonant elements. Two types of compact short-circuited resonators are used; stepped impedance and quarter-wave resonators. The design procedure based on composing the antenna resonators is straightforward and can be applied to design any triple band antenna at three pre-specified bands using simple relations and design curves. The resonator integration has been performed to maintain single feed, reduce the overall antenna size, and preserve the quality-performance at each band. The two designed antennas are simulated, optimized, and realized on RT-Duroid substrate to verify the concept. Simulation and experimental results are in good agreement and demonstrate the performance of both triple band compact antennas.

2009-06-13 PIER Vol. 93, 205-219, 2009. doi:10.2528/PIER09042902

Quasi-Optical Bessel Resonator

Yan-Zhong Yu and Wen-Bin Dou

In this paper, a quasi-optical Bessel resonator (QOBR) for generating approximations to Bessel-type modes at millimeter wavelengths have been designed and analyzed. A design approach is based on the quasi-optical techniques. In order to analyze the designed QOBR rigorously, a new method based on iterative Stratton-Chu formula (ISCF) is developed from the classical Fox-Li algorithm. And its validity is demonstrated. Numerical results reveal that at the output plane the intensity distributions of the Bessel-type modes of the QOBR are modulated by a bell-shaped envelope, and their phase patterns have a block-shaped profile except slight distortion on the edges of the element due to aperture diffraction. The effect of varying the parameters of the designed QOBR on the relevant output characteristics is also examined in our study.

2009-06-13 PIER Vol. 93, 189-203, 2009. doi:10.2528/PIER09042212

Thickness-Independent Complex Permittivity Determination of Partially Filled Thin Dielectric Materials into Rectangular Waveguides

Ugur Cem Hasar

A microwave method has been proposed for accurate complex permittivity measurement of thin dielectric materials partially filling the waveguide. The method employs propagation constant measurements at two locations of the sample inside its holder. It increases the accuracy of permittivity measurements of similar methods in the literature since it utilizes the measurements of the distances between the inner waveguide walls and sample lateral surfaces instead of directly measuring the sample thickness. It has been validated by comparing the measured complex permittivity of a thin Plexiglas sample by the proposed method with that of the method in the literature.

2009-06-13 PIER Vol. 93, 177-188, 2009. doi:10.2528/PIER09042202

X-Band Miniaturized Wideband Bandpass Filter Utilizing Multilayered Microstrip Hairpin Resonator

Helmi Adam, Alyani Ismail, Mohd Adzir Mahdi, Mohammad Shahrazel Razalli, Adam Reda Hasan Alhawari, and Babak Kazemi Esfeh

This paper presents a new design of miniaturized wideband bandpass filter using microstrip hairpin in multilayer configuration for X-band application. The strong coupling required for wideband filter is realized by arranging five hairpin resonators in two layers on different dielectric substrates. Since adjacent resonator lines are placed at different levels, there are two possible ways to change coupling strength by varying the overlapping gap between two resonators; vertically and horizontally. In this paper, simulated and measured result for a wideband filter of 4.4 GHz bandwidth at 10.2 GHz center frequency with fifth order Chebyshev response is proposed. The filter is fabricated on 0.254 mm thickness R/T Duroid 6010 and R/T Duroid 5880 with dielectric constant 10.2 and 2.2 respectively using standard photolithography technique. Two filter configurations based on vertical (Type 1) and horizontal (Type 2) coupling variation to optimize the coupling strength are presented and compared. Both configurations produce very small and compact filter size, at 5.0 x 14.6 mm2 and 3.2 x 16.1 mm2 for the first and second proposed filter type respectively. The measured passband insertion losses for both filters are less than 2.3 dB and the passband return loss is better than -16 dB for filter Type 1 and -13 dB for filter Type 2. Very small and compact filter is achieved where measured results show good agreement with the simulated responses.

2009-06-13 PIER Vol. 93, 161-176, 2009. doi:10.2528/PIER09041405

A New Microwave Method Based on Transmission Scattering Parameter Measurements for Simultaneous Broadband and Stable Permittivity and Permeability Determination

Ugur Cem Hasar

A new microwave method has been proposed for simultaneous broadband and stable complex permittivity and complex permeability determination of magnetic and nonmagnetic materials. The method utilizes complex transmission scattering measurements at different frequencies. For a change in constitutive parameters determination, we considered zero-order and higher-order approximations. We have verified the proposed method from measurements of two medium- and low-loss materials with another method and available reference data in the literature.

2009-06-13 PIER Vol. 93, 145-160, 2009. doi:10.2528/PIER09041303

Synthesis of Planar Arrays Using a Modified Particle Swarm Optimization Algorithm by Introducing a Selection Operator and Elitism

Marta Lanza Diego, Jesus Ramon Perez Lopez, and Jose Basterrechea

A modified particle swarm optimization (PSO) algorithm applied to planar array synthesis considering complex weights and directive element patterns is presented in this paper. The modern heuristic classical PSO scheme with asynchronous updates of the swarm and a global topology has been modified by introducing tournament selection, one of the most effective selection strategies performing in genetic algorithms the equivalent role to natural selection, and elitism. The modified PSO proposed combines the abilities of the classical PSO to explore the search space and the pressure exerted by the selection operator to speed up convergence. Regarding the optimization problem, the synthesis of the feeds for rectangular planar arrays consisting of microstrip patches or subarrays of microstrip patches is considered. Results comparing the performance and limitations of classical and modified PSO-based schemes are included considering both test functions and planar array complex synthesis to best meet certain far-field radiation pattern restrictions given in terms of 3D-masks. Finally, representative synthesis results for sector antennas for worldwide interoperability for microwave access (WiMAX) applications are also included and discussed.

2009-06-12 PIER Vol. 93, 125-143, 2009. doi:10.2528/PIER09033003

Slot Antenna on a Conducting Elliptic Cylinder Coated by Nonconfocal Chiral Media

Biglar Najjar-Khatirkolaei and Abdel Sebak

The characteristics of a slot antenna on a perfectly conducting elliptic cylinder coated by nonconfocal chiral media are investigated. The structure is fed with a line source or plane wave. The analysis is carried out by expressing the fields in and around the cylinder in terms of Mathieu and modified Mathieu functions using the separation of variable and exact boundary value technique. The unknown aperture field is expressed in terms of Fourier series with unknown expansion coefficients. The expansion coefficients are found by applying the boundary conditions on different surfaces and employing the addition theorem and orthogonality properties of the Mathieu functions. For TM and TE cases some numerical results of the antenna gain for co- and cross-polarized waves are presented and discussed.

2009-06-11 PIER Vol. 93, 107-124, 2009. doi:10.2528/PIER09040908

Direct Radiating Arrays for Satellite Communications via Aperiodic Tilings

Andrea Francesco Morabito, Tommaso Isernia, Maria Grazia Labate, Michele Durso, and Ovidio Mario Bucci

This paper presents an innovative Direct Radiating Array (DRA) architecture exploiting aperiodic tilings of the plane. In particular, a pinwheel tiling has been selected in order to fix positions of the different radiating sources, which are constituted by properly shaped elements. Such a choice allows to achieve a good aperture efficiency and very low pseudo-grating lobes while using only two different kinds of radiating elements. Preliminary results are shown and discussed with reference to both cases wherein the single tiles are not fully populated and wherein ad-hoc sub-array radiators are used. The very encouraging results achieved leave open the way for further interesting possibilities.

2009-06-10 PIER Vol. 93, 91-105, 2009. doi:10.2528/PIER09050604

The Combination of Bcgstab with Multifrontal Algorithm to Solve Febi-MLFMA Linear Systems Arising from Inhomogeneous Electromagnetic Scattering Problems

Xue Wei Ping, Tie-Jun Cui, and Wei Bing Lu

The hybrid finite-element/boundary-integral method (FEBI) combined with the multilevel fast multipole algorithm (MLFMA) has been applied to model the three-dimensional scattering problems of inhomogeneous media. The stabilized Bi-conjugate gradient (BCGATAB) iterative solver based on the inner-looking algorithm is proposed to solve the final FEBI linear system, and the multifrontal algorithm combined with the approximate minimal degree permutation (AMD) is used for the LU decomposition of the FEM matrix. The accuracy and efficiency of the combined algorithm has been validated in the final of the paper. Numerical results show that the proposed method can greatly improve the efficiency of FEBI for scattering problems of inhomogeneous media.

2009-06-04 PIER Vol. 93, 71-90, 2009. doi:10.2528/PIER09040105

Filtering Lens Structure Based on Srrs in the Low THz Band

Belen Andres-Garcia, Luis Enrique Garcia-Munoz, Vicente Gonzalez-Posadas, Francisco Javier Herraiz-Martinez, and Daniel Segovia-Vargas

A filtering lens for conical horns based on Metamaterials is presented. The paper focuses on a millimeter wave application. The metamaterial structure is composed of a printed layer of Split Ring Resonators (SRRs) on a substrate. The structure is used as a superstrate on the horn aperture. When the SRRs are excited, a filter performance arises preventing radiation in the desired frequency bands. Besides the filtering property, also a lens behavior is achieved. In this way larger gain can be achieved in both E and H planes, reducing the 3 dB beamwidth. A 6% -3 dB stop band is achieved from 73.3 GHz to 85.7 GHz. Symmetrisation of the radiation pattern up to 3 dB is accomplished and the focalization effect is achieved by emulating a hyperbolical-plane lens. Thus, a simplified system based on a conical horn can be designed by unifying the filter and lens in one electromagnetic element.

2009-06-03 PIER Vol. 93, 57-70, 2009. doi:10.2528/PIER09033001

A Breast Imaging Model Using Microwaves and a Time Domain Three Dimensional Reconstruction Method

Hui Zhou, Takashi Takenaka, Jessi Johnson, and Toshiyuki Tanaka

An iterative reconstruction algorithm for three-dimensional (3-D) microwave tomography by using time-domain microwave data is applied to detect breast tumor. A numeric breast model with randomly distributed glandular tissues (random size and permittivity) with a tumor is designed for the calculation of synthetic microwave data. An "air phantom" consisting of a section of polyvinyl chloride (PVC) pipe filled with styrofoam and a thin glass cylinder is constructed for collecting microwave data in laboratory. The "breast" and "air phantom" are reconstructed. Reconstruction results show that the "tumor" in the breast is clearly reconstructed, and the glass cylinder is successfully reconstructed too.

2009-06-01 PIER Vol. 93, 41-56, 2009. doi:10.2528/PIER09021909

Microstrip Square Ring Antenna for Dual-Band Operation

Subhrakanta Behera and Kalarickaparambil Vinoy

This paper presents a generalized approach to design an electromagnetically coupled microstrip ring antenna for dual-band operation. By widening two opposite sides of a square ring antenna, its fractional bandwidth at the primary resonance mode can be increased significantly so that it may be used for practical applications. By attaching a stub to the inner edge of the side opposite to the feed arm, some of the losses in electrical length caused by widening can be regained. More importantly, this addition also alters the current distribution on the antenna and directs radiations at the second resonant frequency towards boresight. It has also been observed that for the dual frequency configurations studied, the ratio of the resonant frequencies (fr2/frr) can range between 1.55 and 2.01. This shows flexibility in designing dual frequency antennas with a desired pair of resonant frequencies.

2009-05-29 PIER Vol. 93, 29-40, 2009. doi:10.2528/PIER09042104

Geometry Based Preconditioner for Radiation Problems Involving Wire and Surface Basis Functions

Marta Gomez Araujo, Jose Manuel Bertolo, Fernando Obelleiro, Jose Luis Rodriguez, Jose Taboada, and Luis Landesa

An innovative preconditioner has been developed in this work. It significantly improves the convergence of the iterative solvers applied to electromagnetic radiation problems by a renormalization of the matrix equation. The preconditioner balances the disparities in terms of magnitude and units caused by the strong self-coupling of the antennas, the non-uniformity of the meshes and also by the coexistence of wire and surface basis functions. It can be easily integrated into different electromagnetic solvers with a negligible impact on the computational cost on account of its simple implementation.

2009-05-28 PIER Vol. 93, 13-28, 2009. doi:10.2528/PIER09030804

Bistatic RCS Prediction for Complex Targets Using Modified Current Marching Technique

Xiao-Feng Li, Yong-Jun Xie, and Rui Yang

The improved high-frequency method for solving the bistatic scattering from electrically large conductive targets is presented in this paper. Since the previous physical optical methods overlooked the current impact of shadow zone and led to the increasing problems of the large angle bistatic calculation, the improved method is deduced by introducing the current marching technique into the conventional physical optical method. Combined with the graphical-electromagnetic computing method that extracted the illuminated and shadow facet in accordance with the direction of the incident sort iteration, one may calculate the bistatic radar cross-section of a conductive targets object. The numerical results show that this method is efficient and accurate.

2009-05-28 PIER Vol. 93, 1-12, 2009. doi:10.2528/PIER09050412

Experimental Demonstration of Metamaterial-Based Phase Modulation

Iftekhar Mirza, Jerico N. Sabas, Shouyuan Shi, and Dennis W. Prather

Phase modulation is critical due to its applicability in varied RF devices such as phased array antennas, radars to name a few. In this paper, we report experimental data on phase modulation in the X-band frequency using tunable metamaterials such as a planar design of stacked dual split ring resonators (DSRRs) of 3mm thickness at 8.5 GHz. Modulation was brought about by switching between the open and closed states of the rings causing a net change in the effective refractive index and thereby producing a phase variation. One and two dimensional free-space scanning experiments were carried out where a phase modulation of 62 degrees was demonstrated. The measured data matched well with the numerically simulated results.